Prosthetic heart valves are used to replace diseased natural heart valves in the aortic, mitral, tricuspid and pulmonary positions in the heart. Examples of three such valves are shown in Carpentier et al U.S. Pat. No. 4,106,129, Ionescu et al U.S. Pat. No. 4,084,268 and Davis et al U.S. Pat. No. 4,192,020. As shown by these patents, a prosthetic heart valve typically includes a frame formed of a wire or a shell and valve leaflets attached to the frame.
One of the major problems with prosthetic leaflet heart valves, including bioprosthetic valves, is insufficient long-term durability resulting from failure of the valve leaflets in the area of their attachment to the frame. Many different attachment techniques have been attempted, including stitching, gluing, integral and dip molding, clamping and combinations of these methods.
Stitching was the earliest method used to attach the valve leaflets in a prosthetic heart valve; however, disruption of the leaflet material at the suture lines produced a number of failures Gluing has not proved reliable and it is generally used in conjunction with other methods, such as clamping or stitching. Integral molding has also proven to be not reliable, and dip molding is not preferred because it can only be used with certain materials, such as polyurethane. An additional disadvantage of integral molding is that it cannot be used with biological materials because of the high temperatures involved in the molding process.
One reason for failure of the valve leaflets is that, during diastole in the aortic position and systole in the mitral position, a radial inward tensile force is applied to the valve leaflets. This tensile force imposes loads on whatever leaflet attachment means is utilized and can ultimately be destructive. For example, when stitching is utilized, the tensile force imposes high shear stress which can ultimately result in valve leaflet failure.